1. Field of the Invention
This invention relates to the field of synchronized shifting among various speed ratios of a multiple speed tractor transmission. More particularly, the invention pertains to accelerating a tractor load at very low speed through operation of a dry friction clutch.
2. Description of the Prior Art
Tractor gear boxes produce a large number of gear ratios within a transmission mechanism located between the engine and the final drive differential mechanism. In the conventional design, a first gear arrangement produces a range of speed reduction of the output of a first gear set in relation to the speed of the engine. Typically, the torque delivery path of such a transmission includes a creeper speed mechanism located behind the first gear set and before the differential mechanism. The range speed mechanism produces an additional speed reduction between the output of the transmission gear set and the output of the range speed mechanism.
In the operation of a conventional tractor transmission, the vehicle accelerates the load from stop as the vehicle operator shifts the transmission from the lowest gear ratios to the higher gear ratios. His control of the speed of the vehicle for a given engine speed must therefore change in accordance with the predetermined gear ratio of the transmission gear set and range speed mechanism.
However, it would be preferable, especially at the lowest vehicle speeds, if the operator were able to control manually the speed and rate of acceleration of the vehicle over a continuous, stepless speed range determined by the operator in accordance with the requirements of the work being performed. Thereafter, when the speed of the vehicle has been increased sufficiently, the vehicle operator could discontinue manuel speed control and return control of the vehicle speed to the predetermined ratios of the transmission gear set and range speed mechanism.